In recent years, semiconductor technology has created the possibility of a miniature gas chromatograph. Such a device is described in U.S. Pat. No. 4,474,889, issued to Terry et al., in which the channels for the carrier gas and sample gas are etched in a semiconductor wafer. The analytical column is external to these elements. U.S. Pat. No. 4,471,647, issued to Jerman et al., discloses a miniature gas chromatograph in which all of the channels, including the column, are etched on a semiconductor wafer.
Functionally, a gas chromatograph can be divided into elements which may be used repeatedly, for any tests, and elements which may need to be changed, depending on the gases to be detected. The former group includes the injector and detector and their associated valves and channels. On the other hand, the column may need to be changed in order to permit the gas chromatograph to analyze a different gas or group of gases.
The miniaturization of gas chromatographs has led to the use of miniaturized capillary columns having internal diameters generally in the range of 100-500 microns. Exchanging a column having these dimensions is no trivial task, and one that normally cannot be performed in the field. Frequently, the chromatograph must be returned to the manufacturer, who severs the connections to the analytical and reference lines at the injector and detector, replaces the column, and then reconnects the column to the injector and the detector. Aligning the tubes on either side of the connection is a delicate operation, and connectors containing ferrules are often used for this purpose. A mismatch or the introduction of a "dead volume" in the connector can create eddy currents and spatial voids which enhance Brownian diffusion, ultimately interfering with the accuracy of the analysis. This process can be time consuming and obviously requires the chromatograph to be removed from service. It also involves some expense and training.